This invention relates to the production of metallic powders. More particularly, it relates to a metallic powder and process for producing a metallic powder by reducing a solubilized or liquid metal compound by contacting it with the pyrophoric surface of a reactive metal powder.
Conventionally, various techniques exist for the production of metal powders. These include atomization, grinding, gaseous reduction of oxides, gaseous reduction of solutions, reduction with carbon, carbonyl decomposition and electrolytic methods.
In the case of aluminum, powdered metal may be obtained by atomization or by milling larger particles of aluminum, both methods being well known in the art.
Several pure metals and many alloys are produced commercially in large quantities by aluminothermic reduction, also known as the thermite process. In this process, aluminum is melted in contact with other metal ores, resulting in oxidation of aluminum and reduction of the ore. The reduced metal is usually obtained as an undivided lump assuming the form of the reaction vessel. Aluminothermic reactions require initial high temperatures to melt the aluminum and start the reaction; the reaction itself generates additional heat which is generally sufficient to melt the reduced metal if its melting point is higher than that of aluminum. By means of the techniques described in this invention, such reductions are carried out at temperatures far below that at which aluminum melts and are carried out successfully even at ambient temperature. Quite surprisingly, the reduced metal assumes a powder form, so that this technique represents a novel alternate method for producing metal powders.
It is known from my previous U.S. Pat. No. 3,890,166 that the milling of aluminum produces pyrophoric surfaces capable of reacting with other compounds. My previous U.S. Pat. No. 3,853,931 describes the manufacture of aluminum hydrocarbyls by adding hydrogen and an olefin or aluminum hydrocarbyl compound to an autoclave containing an activated slurry of pyrophoric aluminum powder in benzene.